Project Abstract and Summary Falls and their consequences are among the major problems in the medical care of older individuals. With advancing age, the capacity to maintain balance after perturbations deteriorates due to a number of age- related sensorimotor deficits, and likely increases the risk for falls. The unexpected nature of falls triggers startle-like whole body postural responses. Startle responses are characterized by exaggerated whole body postural responses with increased muscle co-activity causing co-contraction during the first trial response (FTR) and normally diminish with repeated exposure due to behavioral habituation. Because all falls involve a downward motion of the body with gravity which may trigger a startle response, understanding whether these responses are also superimposed onto the landing response will be important to determine. Our central hypothesis is that age-related abnormalities of exaggerated startle responses and habituation will influence the initial landing response to a sudden loss of the ground support surface but can adapt due to the modulatory effects of motor prediction and participant awareness. Understanding whether the FTR during sudden drop perturbations influences the landing response will be important to determine whether or not it enhances balance recovery or is problematic and precipitates falls. Moreover, identifying whether the effects of age- associated abnormalities on landing movements during FTR can be modulated using motor prediction and participant awareness will help direct future interventions aimed at fall prevention. Whole body postural muscle activation patterns, movement kinematics, and landing impact forces will be assessed by electromyographic (EMG) recordings, motion capture, and force platform recordings. The specific aims are 1) Compare changes in landing responses to unexpected and expected drop perturbations in relation to age during a) FTRs and b) subsequent trials; and 2) Determine the modulatory effects of repeated expected drop perturbations on reducing FTR magnitude evoked by unexpected drop perturbations in young and older adults. Expected outcomes are that abnormal neurophysiological mechanisms causing excessive startle contributions to postural FTRs with older age will be linked with changes in landing control mechanisms. Moreover, demonstrating the capacity to adapt landing responses through behavioral habituation will direct future interventions aimed at improving landing strategies to attenuate the impact of falls.